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Amaranthaceae ( ) is a family of commonly known as the amaranth family, in reference to its type genus Amaranthus. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 species, making it the most species-rich lineage within its parent order, Caryophyllales.
The Leaf are simple and mostly alternate, sometimes opposite. They never possess . They are flat or terete, and their shape is extremely variable, with entire or toothed margins. In some species, the leaves are reduced to minute scales. In most cases, neither basal nor terminal aggregations of leaves occur.
The are solitary or aggregated in cymes, Raceme, or and typically perfect (bisexual) and actinomorphic. Some species have unisexual flowers. and are either herbaceous or scarious. Flowers are regular with an herbaceous or scarious perianth of (one to) mostly five (rarely to eight) , often joined. One to five are opposite to tepals or alternating, inserting from a hypogynous disc, which may have appendages (pseudostaminodes) in some species. The have two or four pollen sacs (). In tribe Caroxyloneae, anthers have vesicular appendages. The pollen grains are spherical with many pores (pantoporate), with pore numbers from a few to 250 (in Froelichia). One to three (rarely six) are fused to a superior ovary with one (rarely two) basal ovule. Idioblasts are found in the tissues.
The diaspores are or (utricles), more often the perianth persists and is modified in fruit for means of dispersal. Sometimes even bracts and bracteoles may belong to the diaspore. More rarely the fruit is a circumscissile capsule or a berry. The horizontal or vertical seed often has a thickened or woody seed coat. The green or white embryo is either spirally (and without perisperm) or annular (rarely straight).
In phytochemical research, several methylenedioxyflavonols, saponins, triterpenoids, ecdysteroids, and specific root-located carbohydrates have been found in these plants.
The multiple origin of photosynthesis in the Amaranthaceae is regarded as an evolutionary response to inexorably decreasing atmospheric levels, coupled with a more recent permanent shortage in water supply as well as high temperatures. Species that use water more efficiently had a selective advantage and were able to spread out into arid habitats.
The family Amaranthaceae was first published in 1789 by Antoine Laurent de Jussieu in Genera Plantarum, p. 87–88. The first publication of family Chenopodiaceae was in 1799 by Étienne Pierre Ventenat in Tableau du Regne Vegetal, 2, p. 253. The older name has priority and is now the valid scientific name of the extended Amaranthaceae ( s.l. = sensu lato).
Some publications still continued to use the family name Chenopodiaceae. Phylogenetic research revealed the important impact of the subfamily Polycnemoideae on the classification (see cladogram): if Polycnemoideae are considered a part of Chenopodiaceae, then Amaranthaceae ( s.str. = sensu stricto) have to be included, too, and the name of the extended family is Amaranthaceae. If Polycnemoideae would be separated as its own family, Chenopodiaceae and Amaranthaceae ( s.str.) would form two distinct monophyletic groups and could be treated as two separate families.
Amaranthaceae ( s.l.) includes the former families Achyranthaceae , Atriplicaceae , Betaceae , Blitaceae , Celosiaceae , Chenopodiaceae nom. cons., Corispermaceae , Deeringiaceae , Dysphaniaceae nom. cons., Gomphrenaceae , Polycnemaceae , Salicorniaceae , Salsolaceae , and Spinaciaceae .
The systematics of Amaranthaceae are the subject of intensive recent research. Molecular genetic studies revealed the traditional classification, based on morphological and anatomical characters, often did not reflect the phylogenetic relationships.
The former Amaranthaceae (in their narrow circumscription) are classified into two subfamilies, Amaranthoideae and Gomphrenoideae, and contain about 65 genera and 900 species in tropical Africa and North America. The Amaranthoideae and some genera of Gomphrenoideae were found to be polyphyletic, so taxonomic changes are needed.
Current studies classified the species of former Chenopodiaceae to eight distinct subfamilies (the research is not yet completed): Polycnemoideae, which are regarded as a basal lineage, Betoideae, Camphorosmoideae, Chenopodioideae, Corispermoideae, Salicornioideae, Salsoloideae, and Suaedoideae. In this preliminary classification, the Amaranthaceae s.l. are divided into 10 subfamilies with approximately 180 genera and 2,500 species.
Dysphania ambrosioides (epazote) and Dysphania anthelmintica are used as medicinal herbs. Several amaranth species are also used indirectly as a source of soda ash, such as members of the genus Salicornia (see glasswort).
A number of species are popular garden , especially species from the genera Alternanthera, Amaranthus, Celosia, and Iresine. Other species are considered , e.g., redroot pigweed ( Amaranthus retroflexus) and alligatorweed ( Alternanthera philoxeroides), and several are problematic invasive species, particularly in North America, including Salsola tragus and Bassia scoparia. Many species are known to cause pollen allergies. List of allergic plants in family Chenopodiaceae at pollenlibrary.com
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